Physical–Chemical Aspects of Modifying Cement Systems with Individual and Complex Plasticizing Admixtures

Abstract

The research findings of rheological properties of cement systems, modified with plasticizing mono-admixtures, containing adsorption-active groups of various natures, and with complexes, based on them, are presented. It has been demonstrated that the cement paste’s rheology can be efficiently regulated not only by changing the chemical composition and structure of modifiers, but also by combining the types and amounts of active admixtures of polar organic substances with various molecular weight. It has been determined that the alteration of hydrophilic groups’ nature by replacing sulfo-groups with hydroxyl groups increases the admixture’s plasticizing activity, which is both due to the higher hydrophilic ability of phenolic hydroxyl groups, and to their lower molecular weight. The inverse proportion between the cement paste mini-cone flow and its yield point has been identified, characterized with the minor alteration of d at the considerable initial alteration of τ₀ and indicating that after the equilibrium is reached, the gravity force is balanced with cement suspension’s particles interaction force. Experimental data indicate that the nature of the plasticizing admixture’s hydrophilic groups influences such its properties, as plasticizing ability, plasticizing activity and selectivity; with that, hydroxyl groups provide the better properties of the admixture, in comparison with sulfo-groups.